1. Field of the Invention
This invention pertains to directional boring machines. More particularly, this invention pertains to a directional boring machine with a novel duckbill for facilitating penetration of the earth.
2. Description of the Prior Art
Directional boring machines are well known. An example of such a machine is shown in U.S. Pat. No. 4,953,638.
In directional boring machines, a plurality of pipe segments are threadedly interconnected to form a drill string. A terminal end of the drill string is provided with a drill head. An above-ground end of the drill string is rotated and longitudinally advanced by a boring machine. Through manipulation of the boring machine, the drill head can be forced through the earth to form a bore. Drill heads come in a variety of shapes and configurations.
The '638 patent shows a particular design of a drill head which includes a metal plate (item 72 in FIG. 6) attached to a drill head where the metal plate extends forwardly from the drill head. In the industry, such a metal plate is referred to as a duckbill. The duckbill assists in penetrating the earth as the drill string is rotated. Further, the angled inclination of the duckbill relative to the axis of rotation of the drill head encourages the drill string to be moved in a curved direction when the drill head is being longitudinally advanced without rotation.
Underground directional boring machines are used to form bores through a wide variety of soil conditions. Flat duckbills such as that shown in FIG. 6 of the '638 patent are adequate for soft soil conditions. However, such drill heads may not be satisfactory for rock or other hard soil conditions. In such conditions, it would be desirable to provide additional cutting teeth on the duckbill to facilitate cutting through the soil conditions. An example of a duckbill with cutting members is shown in U.S. Pat. No. 5,148,880 in FIGS. 29-31.